1. Field of the Invention
This invention relates to an automatic focus detecting apparatus.
2. Description of the Prior Art
There are single lens reflex cameras of the type in which the light from an object passed through a phototaking lens is directed to the light-receiving portion of a focus detecting unit by an optical system such as a quick return mirror. In such cameras, during exposure of film, the optical system is moved to make the light-receiving portion dark. After completion of the exposure, the optical system is returned to its original position and the object light again enters the light-receiving portion, but if the object brightness is low, there is a disadvantage that the focus detecting unit is unstable for a long period and effects improper focus detection display and automatic focus adjustment operation during this period. Not only the TTL type automatic focus detecting apparatus, as described above, but also an automatic focus detecting apparatus of the type which carries out focus detection from the information of the object light, suffers from a disadvantage that if the object brightness is low, even upon the closing of the main switch, the apparatus remains unstable for a long period and effects improper focus detection display and automatic focus adjustment operation during this period.